The present invention is directed to a publication distribution system and, more specifically to a computer operated feedback control system for controlling a process such as a paper-making machine.
FIG. 1 illustrates a prior control process which while specifically related to the paper-making industry might occur in any type of computer control system where several sources of data (termed a Publisher) is desired by several Subscribers. As illustrated in FIG. 1, as specifically applied to the paper-making industry, there is a central computer 10 where in a star-type system having the data path 11, 12 and 13 all of which go to the input port, indicated generally at 14 of the computer. Thus, this may be a choke point or bottleneck in the system. On data line 13, a so-called Publisher in the form of sensors sense among other parameters of a paper-making process, moisture and basis weight. This is usually done by scanners which scan in a cross direction across the width of the paper being manufactured and provides data for every xe2x80x9cslicexe2x80x9d of the paper. Thus, for every scan there is a significant data output. To control moisture and basis weight to desired set points and provide quality control, the feedback control system and computer 10 receives this data and by the use of actuators 17 and 18 on the data lines 11 and 12 individually control basis weight (for example, the headbox openings of the paper-making machine are controlled) or moisture (see actuator 18). Moisture may be controlled in several ways by controlling steam valves or actually spraying water on the paper sheet. In addition, there are other parameters such as caliper and gloss of the paper which can be controlled in the same feedback control manner. Thus, in summary with the prior art star system of FIG. 1 there is a large amount of data going to the central computer and a single node of the computer must listen to all of the communications coming from each of the legs of the star, that is, 11, 12 and 13. And in the case of sensors 16 since data is normally polled, the whole array of data is transferred; that is, for each scan an entirely new array of data must be transferred and processed.
It is therefor a general object of the present invention to provide an improved publication distribution system.
In accordance with the above object, there is provided a computer operated feedback control system for controlling a process comprising an effective common data bus. A plurality of Publisher means is connected to the data bus for sensing a variable parameters of the process and respectively storing data related to such parameter. A plurality of Subscriber means is connected to the data bus for receiving data from a selected Publisher means. Means are provided for transmitting to the Subscriber means from the selected Publisher means only that portion of data which has been changed from a value prior in time.